This disclosure pertains to stage apparatus as used, for example, in microlithography systems. Microlithography involves transfer-exposure of a pattern, usually defined on a reticle (also termed a xe2x80x9cmaskxe2x80x9d), to a lithographic substrate such as a semiconductor wafer. Microlithography is a key technology used in the fabrication of microelectronic devices such as integrated circuits, displays, micromachines, and the like. More specifically, the disclosure pertains to stage apparatus that perform high-precision positioning with minimal generation of magnetic-field fluctuations.
Most contemporary microlithography is xe2x80x9copticalxe2x80x9d microlithography, which is performed using deep-ultraviolet light. To achieve greater pattern-transfer resolution, other microlithography technologies are under active development, including charged-particle-beam (CPB) microlithography (e.g., electron-beam microlithography) and xe2x80x9cextreme ultravioletxe2x80x9d (EUV) microlithography. In view of the extremely high accuracy with which any of these microlithography techniques must be performed, it is imperative that the reticle (if a reticle is used) and the lithographic substrate be mounted on respective stage apparatus capable of providing high-accuracy movement and positioning of the reticle and substrate relative to each other and relative to the optical system of the microlithography tool. To such end, each such stage apparatus comprises one or more xe2x80x9cactuatorsxe2x80x9d that move a respective stage platform on which the reticle or substrate, respectively, is mounted.
For example, an electron-beam microlithography tool typically comprises a reticle stage and a substrate stage. The electron beam propagates in a vacuum through an electron-optical system that comprises electron lenses, deflectors, and the like, and that is situated relative to the reticle and substrate stage apparatus. In the electron-optical system, at least certain of the electron lenses and deflectors converge and deflect, respectively, the beam using magnetic fields. Hence, the beam is easily influenced by magnetic fields and is easily affected in an adverse manner by stray magnetic fields, especially stray magnetic fields associated with the stage apparatus (that are located near the beam trajectory in the tool). For this reason, the actuators usually selected for use in stage apparatus in electron-beam microlithography tools do not generate magnetic fields.
Exemplary actuators currently used in these stage apparatus include ultrasonic actuators and pneumatic actuators. Unfortunately, ultrasonic actuators generate contaminants and tend to outgas in a vacuum environment. Ultrasonic actuators also have poor reliability and tend to produce troublesome vibrations. Pneumatic actuators can exhibit a positioning accuracy that is less than desired, as caused by the characteristically non-linear response characteristics of these actuators, especially accompanying changes in actuator temperature.
Electromagnetic linear motors, in contrast, have high reliability, are easily controlled, produce low vibrations, and exhibit high positioning accuracy. Linear motors also tend not to exhibit non-linear deviations in operational behavior. Consequently, linear motors commonly are used as the actuators in stage apparatus in optical microlithography tools, especially since the UV light beam is unaffected by stray magnetic fields produced by linear motors. But, magnetic fields produced by linear motors have substantial effects on a charged particle beam. These effects, especially if of a variable nature, can be very difficult to control and/or reduce to insignificant levels. In view of this problem, linear motors conventionally are not favored for use as actuators in stages in CPB-microlithography tools. Nevertheless, in view of the many advantages of linear motors, efforts continue to be directed to the employment of linear motors in stage apparatus used in CPB microlithography tools. An approach to realization of this goal involves magnetically shielding the linear motors. Heretofore, satisfactory magnetic shielding has not been achieved.
The linear-motor concept has been extended to two dimensions for use in xe2x80x9cplanarxe2x80x9d motors, which provide unfettered movement to a stage platform in two dimensions (e.g., X- and Y-dimensions), using a single motor. In this regard, reference is made to Japan Kxc3x4kai Patent Document No. 2001-217183. Planar motors generate substantial magnetic fields. In this reference the planar motor is partially shielded using a rectangular frame member having an L-shaped transverse section. The frame member is disposed in the vicinity of a magnetic pole of the planar motor, and shields some of the magnetic fields that tend to leak from the sides and top of the planar motor. Unfortunately, the realized shielding effect is insufficient.
Electromagnetic linear motors in which the stator comprises a magnetic yoke with permanent magnets and the moving member comprises a moving coil recently have been configured so that the magnetic yoke (which comprises part of the magnetic circuit in the motor) is not magnetically saturated. Such a configuration reduces leaking magnetic fields and provides better motor performance. However, practical use of these linear motors in stage apparatus of an electron-beam microlithography tool requires that additional magnetic-shielding measures be developed in view of the extremely strict magnetic-shielding requirements in such tools.
In view of the shortcomings of the prior art as summarized above, the present invention provides, inter alia, stage apparatus that perform at the requisite high accuracy and precision of stage movement and positioning while satisfactorily suppressing stray magnetic fields that otherwise would significantly perturb, for example, the trajectory of a charged particle beam.
According to a first aspect of the invention, linear motors are provided that comprise a stator, a moving coil, and a magnetic shield. In an embodiment of such a linear motor, the stator includes a yoke that extends in a longitudinal direction and has a U-shaped transverse profile. The stator comprises two parallel linear arrays of permanent magnets mounted to respective inner walls of the yoke and facing each other across a coil-race gap that extends in the longitudinal direction. The yoke has outer surfaces as well as edge regions located adjacent the coil-race gap. The moving coil is situated inside the coil-race gap so as to move, when the moving coil is electrically energized, in the longitudinal direction relative to the arrays of permanent magnets. The magnetic shield extends around, with an intervening space, the outer surfaces of the yoke as well as the edge regions adjacent the coil-race gap, and extends in the longitudinal direction along the length of the yoke.
The magnetic shield desirably is formed as a unitary structure consisting of a single sheet of magnetic-shield material formed so as to conform, with the intervening space, to the outer surfaces of the yoke. The magnetic shield desirably is made of a material selected from the group consisting of Permalloy, soft iron, mild steel, Sendust, and ferrite.
The linear motor further can comprise a coil-mounting member having a T-shaped transverse profile including a stem of the T, wherein the moving coil is mounted on a distal end of the stem of the T. In this configuration, the magnetic shield includes respective lip portions that extend parallel to the stem of the T so as to shield at least a portion of the stem of the T along with the yoke.
The yoke and respective sets of permanent magnets can form individual magnetic loops in the stator that are constrained within the yoke. In this configuration, the magnetic shield effectively contains all stray magnetic fields produced by the stator and moving coil.
According to another aspect of the invention, stage apparatus are provided. An embodiment of such a stage apparatus comprises a guide member, a slider, a stage platform, and a first linear motor. The guide member extends in a longitudinal direction. The slider is guided by the guide member by a non-contacting air bearing situated between the slider and the guide member. The stage platform is mounted to the slider. The first linear motor actuates movement of the slider in the longitudinal direction relative to the guide member. The first linear motor is configured as summarized above.
The stage apparatus further can comprise a second linear motor that actuates, in cooperation with the first linear motor, movement of the slider in the longitudinal direction relative to the guide member, the second linear motor being configured and shielded similarly to the first linear motor. The first and second linear motors desirably apply, in a cooperative manner, a movement force to the slider at a center of gravity of the slider, so as to actuate movement of the slider in the longitudinal direction relative to the guide member.
Another aspect of the invention is directed to methods for magnetically shielding a linear motor, in the manner summarized above.
The foregoing and additional features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.